This study aimed to assess community characteristics of the soil fauna associated with the roots of Deyeuxia arundinacea, as well as with its decomposing litter. Litter bags were used to study the characteristics of the soil fauna from August 2013 to July 2014. In root decomposition bags, 1 321 individual animals belonging to 37 groups of the soil fauna were found, and 958 individuals of 25 groups were found in litter decomposition bags. The decomposing roots had a fauna containing higher numbers of individuals and more groups in each month than that in the litter decomposition bags. The community diversity indices showed the same trends, although the Shannon, Pielou, and Margalef indices decreased as time passed, while the Simpson’s index increased with time. Different parts of Deyeuxia arundinacea had different effects on the number of individuals and groups in the soil fauna. The effects of the interaction between different parts of Deyeuxia arundinacea and month on individual density and biodiversity were non-significant (P > 0.05), but this interaction did significantly affect the number of groups (P < 0.05). A positive correlation was found between both the average temperature and the average rainfall and the number of groups in the soil fauna associated with decomposing roots. A positive correlation was also found between the average temperature and the density of the soil fauna, and between the average temperature and average rainfall with the Shannon and Margalef index values, respectively. A negative correlation was found between both the average temperature and average rainfall and Simpson’s index values. These results indicated that the highest numbers of individuals and groups occurred during the root decomposition process, and that the structure and diversity of the soil fauna community associated with Deyeuxia arundinacea are influenced by hydrographic conditions.